Sen. Robert Menendez of New Jersey is under scrutiny over his ties to a Florida doctor under FBI investigation.

WASHINGTON — Sen. Robert Menendez, the powerful New Jersey Democrat who this week was named chairman of the Senate Foreign Relations Committee, is facing a Senate ethics probe into whether he accepted inappropriate gifts from a wealthy Florida eye surgeon who is under FBI investigation.

The Senate Ethics Committee is conducting a preliminary investigation of two trips Menendez took to a luxury beach resort in the Dominican Republic in August and September 2010 as a guest of Dr. Salomon Melgen, a longtime friend and political donor.

The review comes on the heels of an FBI raid on Melgen's medical offices in West Palm Beach, Fla., on Tuesday night and Wednesday as part of an investigation into what sources called possible Medicaid fraud.

"We are aware of the news reports regarding the FBI raid on Dr. Melgen's office. The Ethics Committee will follow its established procedures in this matter," Sen. Johnny Isakson (R-Ga.), vice chairman of the committee, said in a statement.

The scrutiny is increasing at an awkward time for Menendez, the only Latino among Senate Democrats and a leader in a bipartisan effort to overhaul immigration laws. This week, other top Democrats stood by Menendez. Senate Majority Leader Harry Reid of Nevada called him a friend and an "outstanding senator."

One of South Florida's most prominent eye surgeons, Melgen has given substantial contributions to Menendez and other politicians, mostly Democrats. Last year, he contributed $700,000 to the Majority PAC, which supported Democratic candidates. The group, in turn, spent $582,500 to support Menendez's successful bid for reelection. Melgen has also given $33,700 directly to Menendez.

Officials said Menendez didn't follow Senate rules when he failed to report flights aboard Melgen's private jet as gifts on federal financial disclosure forms, or to pay for them. He wrote a $58,500 check to reimburse Melgen last month after questions arose in the media and after Republicans in New Jersey filed a federal ethics complaint.

Menendez's aides called the failure to pay earlier an inadvertent oversight. Menendez and Melgen have denied any wrongdoing, and they have denounced as false published allegations that they had consorted with prostitutes.

"The senator and the doctor have been friends for 20 years, and it's not uncommon for them to go places together," said Melgen's attorney, Dean L. Wilbur.

Under Senate gift rules, Menendez could have accepted and reported the flights as gifts from a friend — but because they're worth more than $250, he would have had to get permission in advance.

By paying for the trips, even more than two years later, Menendez will probably be able to avoid being charged with an ethics violation, said Melanie Sloan, executive director of the Citizens for Responsibility and Ethics in Washington, a government watchdog group.

"That doesn't mean it's OK," Sloan said. "The guy clearly violated the rules, and he clearly was hoping to get away with it."

A review of records shows Menendez has at times used his role on the Foreign Relations Committee to advocate for Melgen.

In a subcommittee hearing last July, he pressed Commerce and State Department officials for action to help enforce contracts held by U.S. firms in the Dominican Republic, including a seaport security contract granted to a company partially owned by Melgen.

The company, ICSSI, holds a contract, reportedly worth $500 million to $1 billion over 20 years, to X-ray cargo shipped through the Dominican Republic. Business groups there have fought to keep the deal from going into effect, arguing that the fees are too high and would increase their costs.

During the committee hearing, Menendez said the contract would help screen cargo for illicit drugs.

"And they don't want to live by that contract either," he told Francisco Sanchez, undersecretary for international trade at the Commerce Department, and Matthew Rooney, a deputy assistant secretary for the State Department. "... Well, what are we willing to do?"

Menendez's office said Friday that his goal was to curb drug trafficking in the region. "It is a fight from which Sen. Menendez will never back down," said a spokeswoman, Tricia Enright.